Routing facility for a subsea electronics module

ABSTRACT

The invention relates to a routing facility ( 1 ) for a subsea electronics module ( 7 ), comprising on a single circuit board ( 2 ) means ( 5 ) for routing data packets between segments of a differential serial bus, and at least one input/output interface ( 14, 15, 16 ) for digital and/or analogue process values, wherein said process values are accessible via said differential serial bus.

The invention relates to a routing facility for a subsea electronicsmodule (SEM).

Subsea electronics modules are preferably used in subsea control units(SCU), e.g., wellhead control units (WCU), for exploring and exploitinggas and oil fields located at the seabed. Gas and oil fields that areexplored or exploited using electronic communication to the wellheads orto other subsea control units are sometimes called “electronic fields”(e-fields).

Typically, several subsea control units and several sensors are locatedin a vicinity of a respective gas or oil field, and are connected to atopside control site. For this purpose, subsea communication is used.For example, process data are transmitted between the topside controlsite and the subsea control units. In order not to require individualcommunication and power lines for each subsea control unit, the subseacontrol units are arranged on the seabed in a network topology. Onenetwork member is equipped with a modem for subsea communication withthe topside control site. The process data are routed within the networkto reach the respective recipient, e.g. either the topside control siteor a certain subsea electronic module. Usually, a differential serialbus is used for the network.

In prior art, different techniques for subsea communication have beendescribed. On the one hand, there are wired electric or opticalconnections, on the other hand there are wireless connections. The wiredconnections can be subdivided into a first group providing communicationlines for electronic or optical connections separate from electric powerlines, and a second group utilising power lines for electroniccommunications. In the latter case, advantageously no separatecommunication lines are needed.

Known subsea control units require at least two input/output (I/O)interface cards for acquisition and/or output of digital and analogueprocess data. In addition, the known subsea control units require onerouting card for each network/bus member that is to be directlyconnected to them. Hence, if several Slave subsea control units are tobe connected to one subsea Master control unit comprising a modem, thesame number of routing cards has to be installed into the subsea Mastercontrol unit. The number of required cards increases if process data isto be acquired or if a process has to be controlled. These multiplecards are space-consuming and power-consuming.

It is an object of the invention to specify a routing facility for asubsea electronics module by which space and power can be saved withinthe subsea electronics module.

This problem is solved by a routing facility comprising the attributesgiven in claim 1.

Advantageous embodiments of the invention are given in the dependentclaims.

According to the invention, a routing facility for a subsea electronicsmodule comprises, on a single circuit board, means for routing datapackets between segments of a differential serial bus, and at least oneinput/output interface for digital and/or analogue process values,wherein said process values are accessible via said differential serialbus. If such a routing facility is used in a subsea electronics module,power consumption as well as required space are significantly reduced incomparison to a prior art router card in combination with multiple priorart input/output interface cards, as additional input/output cards canbe omitted. In the diction of the invention, the term “input/outputinterface” comprises both one-directional and bi-directional interfaces,i.e., pure input interfaces, pure output interfaces, and combinedinput/output interfaces.

A prototype of a routing facility embodiment has been built, comprisinga preferred total of three one input/output interfaces, namely a digitalinput interface, a digital output interface and an analogue inputinterface. By this embodiment, two conventional input/output interfacecards can be omitted although universal connectability for both types ofdata, digital and analogue, is provided. Therefore, the subseaelectronic module can be constructed very compactly.

In a highly preferred embodiment, the routing facility comprises amicrocontroller, a field programmable gate array (FPGA) and at least tworouter resources as said means for routing, wherein each router resourcecomprises a respective local transceiver for a differential serial busand a respective remote transceiver for the differential serial bus, andwherein each local transceiver is connected with the correspondingremote transceiver and with said field programmable gate array that isable to route data packets between said router resources.

In particular, said transceivers can be half-duplex transceivers forrealizing a PROFIBUS DP differential serial bus. Alternatively, thedifferential serial bus may be a CAN bus.

A high fault tolerance of subsea networks can be reached with anembodiment where each of said remote transceivers is galvanicallyisolated from the corresponding local transceiver, wherein said remotetransceivers are floating and said local transceivers are related to alocal electrical ground, and wherein each of said remote transceiverscomprises active bus termination means and bias means.

Faults and defects due to voltage peaks, potential differences or shortcircuits in a seawater cable can be avoided by this embodiment.

In another embodiment, each of said remote transceivers comprises activebus termination means and bias means. This increases fault tolerance,too, because the remaining bus/network can be kept working even if oneseawater cable is interrupted, for example, if it is accidentally cut.

Preferably, said microcontroller and said field programmable gate arrayare connectable to a main control unit of the subsea electronics modulevia a control bus. This enables fast data exchange between the maincontrol unit and the routing facility, in particular for communicatingdata packets to a modem driven by the main control unit.

Preferably, said router resources provide a variable trans-mission bitrate. The communication speed on the differential bus can thus beadjusted to a communication speed of a link to the topside control side,for example. Such a link may be, for instance, a power line. Inparticular, the bit rate on the differential bus can be set to fullyexploit the actual maximum communication speed of the topside link. Inparticular, in embodiments where the microcontroller and the fieldprogrammable gate array are connectable to a main control unit of thesubsea electronics module via the control bus the bit rate to anyconnected remote slave device can be adjusted via the routing facility.Each routing channel is transparent with respect to the bit rate of thedata passing trough it.

In another embodiment, said control bus is connectable to the maincontrol unit via a plug-and-socket connection. Therefore, the circuitboard can be simply exchanged in case of a defect or a hardware update.In particular, it can be designed as a stackable card such as proposedby the PC104 standard, thus further reducing space consumption.

Of course, the invention also relates to a subsea electronics module fora subsea control unit, the subsea electronics module comprising arouting facility according to the invention.

In the following, the invention is described in further detail withseveral drawings.

FIG. 1 shows a block diagram of the first side of a routing facilitycircuit board.

FIG. 2 shows a schematic side view of the routing facility circuitboard.

FIG. 3 shows a block diagram of the back side of the routing facilitycircuit card.

FIG. 4 shows a block diagram of one router resource.

In all drawings, corresponding parts are denoted by identical referencesigns.

The routing facility 1 shown in a front view in FIG. 1 is a singleprinted circuit board 2 comprising on its first side a microcontroller3, a field programmable gate array 4 and four router resources 5alongside a double D-Sub plug-and-socket connector 6. Theplug-and-socket connector 6 is arranged through the circuit board 2,having an exemplary 104-pin plug on one side of the circuit board 2 anda corresponding socket on the other side. For example, it is a stackablebus connector according to the PC104 standard. This allows for stackingtogether the routing facility 1 card with other cards having the sameconnector type. Such a card stack requires minimal space in a subseaelectronic module 7 of a subsea control unit.

The circuit board 2 has a format according to the PC104 standard, forexample. Via the plug-and-socket connector 6, it can be connected to thecontrol bus 8 of a subsea electronic module (not shown), in particularto a main control unit (not shown) of such a module. The control bus 8is an 8-bit industry standard architecture (ISA) bus in the depictedexample. Alternatively, it may be a wider ISA bus, a PCI bus or an IEEE1394 bus, for example. However, the routing facility 1 can also be usedseparately without a stack. For this purpose, it can alternatively beconnected to a subsea electronic module 7 via a bus according to the I²Cstandard. The routing facility 1, in particular the microcontroller 3,can also be connected to a subsea electronic module via a RS-232 serialinterface (not shown) for maintenance access. The routing facility 1card, i.e., the circuit board 2, may also be used in stand aloneoperation without a PC104 stack. However, if a PC104 connection ispresent, power supply for the routing facility 1 is available from it.It is possible to use other power sources as well, in particular instand alone operation.

Each router resource 5 comprises one half-duplex local transceiver 9 fora differential serial bus and one half-duplex remote transceiver 10 forthe differential serial bus. The differential serial bus is a RS-485PROFIBUS DP in the depicted example. Alternatively, it can be a CAN bus,for example. It is also possible to use full-duplex transceivers 9, 10.The subsea electronic unit 7 can have a Slave of the differential serialbus connected to a topside Master, plus it can provide one or moreindividual differential serial bus Masters that have separate Slavesattached to their router resources 5.

The remote transceivers 10 are galvanically isolated from the remainingparts of the routing facility 1, in particular from the localtransceivers 9. They are provided with active bus termination means (notshown in this figure) and bias means (not shown in this figure). Eachremote transceiver 10 is connected to different pins of a single 44-pinplug 11 providing all external connections. In particular, external busmembers for the differential serial bus can be connected via thedifferent pins of the plug 11. The plug 11 also can be used for a RS-232connection to a serial port of an external PC, in particular in standalone operation of the routing facility 1.

The local transceivers 9 are connected to separate bus ports of thefield programmable gate array 4. Each remote transceiver 9 is suppliedby a respective direct current/direct current converter (not shown inthis figure) that is individually disengageable by the fieldprogrammable gate array 4. Usually, a direct current/direct currentconverter is enabled only if a remote bus member is connected to thecorresponding router resource 5 to save power.

Possible bus members that can be connected to the pins of the plug 11are, for example, other subsea control units, i.e., their electronicmodules 7, or sensors (not shown in this figure) able to provide theirprocess data over the differential serial bus. Such sensors arepreferably deployed outside the subsea control unit, for example in welltrees or on pipelines. The sensors can be seawater sensors, pressuresensors or temperature sensors, for example. These sensors monitor theoil/gas/water production process.

The microcontroller 3 and the field programmable gate array 4 aredirectly connected to the control bus 8, by which they are accessible,for example, from the main control unit of the subsea electronic module7 into which the routing facility 1 card is plugged by theplug-and-socket connector 6. The microcontroller 3 serves for settingthe PC104 address in a register in the field programmable gate array 4,and for enabling PC104 access to the field programmable gate array 4. Itadditionally serves for reading and writing all field programmable gatearray 4 registers and storing the predefined status conditions. Thisenables to enter a predefined status upon power-on.

The field programmable gate array 4 has a hardware implementation of alllogic for decoding of the PC104 interface. It contains the physicalregisters for the commands and responses. The router logic is completelyimplemented in the field programmable gate array 4. There are fourinstances of this logic in the field programmable gate array 4, eachcorresponding to one of the router resources 5, and they are controlledby bits in the command registers. Four bits in a Router Control Registerin the field programmable gate array 4 enable/disable the routerresources 5. If one of the bits is zero, the corresponding routerresource 5 will not pass on data from any direction. If the fieldprogrammable gate array 4 detects a hardware error in the differentialserial bus it automatically shuts down the relevant router resource 5.

A data packet arriving at the field programmable gate array 4 either viathe control bus 8, i.e. from the main control unit of the subseaelectronic module, or from one of the router resources 5, i.e., from anexternal source, is routed by the field programmable array 4 to therespective bus destination given in the data packet header. Fortransmission over the control bus 8, the differential serial bus datapackets are wrapped into control bus 8 packets. The field programmablegate array is responsible for wrapping/unwrapping respective datapackets routed to or from the control bus 8. As the router resources 5are connected to individual ports of the field programmable gate array4, the routing facility 1 works as a switch, resulting in minimal buscollisions.

All router resources 5 can work at variable bit rates from 9600 bit/s upto 10 Mbit/s. The field programmable gate array 4 provides a transparentbit rate with a small delay. It listens for traffic in both ends. Theside that detects traffic first is connected to the other side. Andbecause each transceiver 9, 10 needs two microseconds to turn off itsreceiver and to turn on its transmitter, the field programmable gatearray 4 delays the data packet bit stream with two microseconds by ashift register (not shown).

The individual router resources 5 can serve different Slave networksections with equal or different communication speeds, i.e., bit rates.In a PROFIBUS DP network the DP Master always defines the communicationspeed for all DP Slaves that are connected to this DP Master. The maincommunication channel is with one DP Master located at the topside. Thistopside DP Master is controlling the DP speed and DP protocol busparameters which is distributed to all connected subsea DP Slaves uponDP Master start-up sequence.

The maximum differential serial bus bit rate is determined by thevarious cable characteristics and the length of the various cables ineach differential serial bus network. The chosen bit rate is setmanually by an expert engineer in a Master bus configuration setup. Theconsecutive Master restart is activated, and the connected Slaves,including the router channels, will respond according to the DP Master'snew communication speed. If it is difficult for an expert engineer toplan the communication speed, the Master can be configured withincreased bus bit rate followed by new link resets. In this way it ispossible to find the highest possible bit rate for each differentialserial bus network. This procedure is used in a planned commissioningactivity before a complete system start-up.

In special embodiments providing power line communication via power linemodems, a power line modem may give a read-out of the maximally possiblebit rate via a diagnosis interface after the modem initialisation iscompleted. The expert engineer can use this information to set thehighest possible differential serial bus bit rate on the Master busconfiguration setup.

FIG. 2 shows a schematic side view of the circuit board 2 comprising therouting facility 1 on its upper side. On the second side, threededicated input/output interfaces 12, 13, 14 are arranged, namely adigital input interface 12, a digital output interface 13 and ananalogue input interface 14. Each interface 12, 13, 14 has multipleports 11 for acquiring and outputting process data, respectively.

The input/output interfaces 12, 13, 14 can be seen better in FIG. 3which shows a schematic view onto the back side of the circuit board 2.Arranging the routing facility 1 and input/output interfaces 12, 13, 14on both sides of a single circuit board 2 results in further reductionof power consumption and space consumption, as in prior art threeseparate input/output cards were necessary for this purpose. By therouting facility 1 according to this example, the required number ofcards can be reduced from four (two standard input/output interfacecards, one router card, one custom-made input/output card) to one. Thus,power consumption as well as space consumption are reduced toapproximately one fourth in comparison to prior art. The communicationbit rate is variable, allowing for achieving a maximum bus datatrans-mission speed for each individual subsea installation depending onthe environmental situation. Besides, due to bus termination, bias andgalvanic isolation, the routing facility 1 is insensitive to externaldisturbances such as broken seawater cables or external short circuits.

The input/output interfaces provide universal connectability for digitaland/or analogue process data sources. Digital/analogue signal sourcescan be connected at ports 11. The main control unit (not shown in thisfigure) of the subsea electronic module (not shown in this figure)accesses the input/output interfaces 12, 13, 14 via the control bus 8and the microcontroller 3 to which the interfaces 12, 13, 14 areconnected. In contrast to the router resources 5, they are not directlyconnected to the control bus 8.

The digital input interface 12 can be used, for example, for acquiringthe status of relays, in particular switches and power relays, or thestatus of power sensing circuits. The digital output interface 13 can beused, for example, for setting/clearing the status of such a relay, inparticular power-resetting a remote sensor interface. The analogue inputinterface 14 can be used, for example, for values resulting frominsulation monitoring of seawater electric cables or pressuremeasurement or temperature measurement inside a subsea control unit or apipeline. For instance, the insulation monitoring of power anddifferential serial bus seawater cables may result in analogue voltagescorresponding to resistance values between 100 kOhm and 18 MOhm. Ifinsulation is damaged, the resistance value will significantly drop.This can be detected by the microcontroller 3 in the digitized voltagevalues, whereby the respective router resource (not shown in thisfigure) can be disabled. The analogue input interface 14 comprises anexemplary 16-bit analogue-to-digital converter. All input values arebuffered for the microcontroller 3 to read them out and process themfurther. For example, the microcontroller 3 can either reply thedigital/digitized values to time-based queries of the topside controlsite, or it may itself monitor the values and only report deviationsfrom predefined tolerable value intervals.

The digital/digitized values can be stored in registers of the fieldprogrammable gate array (not shown in this figure) in the form ofdifferent ring loops by the microcontroller 3. From there, the valuescan be read out by other bus members, in particular by the topsidecontrol site (not shown in this figure).

FIG. 4 shows one of the router resources 5 in the form of a blockdiagram. The local transceiver 9 is located on the right side and isconnected to the field programmable gate array 4. The remote transceiver10 is located on the left side. Three optocouplers 15 provide galvanicisolation for the remote transceiver 10. Floating power for the remotetransceiver 10 is supplied by a direct current/direct current converter16. The local transceiver 9 is related to ground of the subseaelectronic module 7. The transceivers 9, 10 are designed for a maximumbit rate of 10 Mbit/s. The optocouplers 15 are designed for a maximumbit rate of 25 Mbit/s.

Each router resource 5 has an error detector (not shown) that monitorsthe incoming voltage levels at both the local side and the remote side.If the voltages of the two lines of one side differ about more than apredefined difference for more than 10 bits at the lowest bit rate of9600 bit/s, the respective router resource 5 is disabled. One of eightstatus bits in a Router Status Register in the field programmable gatearray is set to indicate which router resource 5 and on which side(local/remote) the problem is located. By writing a ‘1’ into a statusbit indicating an error, the error is cleared and the correspondingerror detector is re-armed.

A respective control bit in the Router Control Register of the fieldprogrammable gate array 4 corresponds to each direct current/directcurrent converter 16. If a bit is zero, the corresponding directcurrent/direct current converter 16 is disengaged, otherwise it isenabled. Therefore, power can be saved by only enabling directcurrent/direct current converter 16 actually having attached another busmember.

1. A routing facility for a subsea electronics module, comprising on asingle circuit board: means for routing data packets between segments ofa differential serial bus, and at least one input/output interface forat least one of digital and analogue process values, wherein saidprocess values are accessible via said differential serial bus.
 2. Therouting facility according to claim 1, comprising a total of threeinput/output interfaces, namely a digital input interface, a digitaloutput interface and an analogue input interface.
 3. The routingfacility according to claim 1, comprising as said means for routing: amicrocontroller a field programmable gate array and at least two routerresources, each router resource comprising a respective localtransceiver for a differential serial bus and a respective remotetransceiver for the differential serial bus, wherein each localtransceiver is connected with the corresponding remote transceiver andwith said field programmable gate array that is able to route datapackets between said router resources.
 4. The routing facility accordingto claim 1, wherein each of said remote transceivers is galvanicallyisolated from the corresponding local transceiver, wherein said remotetransceivers are floating and said local transceivers are related to alocal electrical ground, and wherein each of said remote transceiverscomprises active bus termination means and bias means.
 5. The routingfacility according to claim 1, wherein said microcontroller and saidfield programmable gate array are connectable to a main control unit ofthe subsea electronics module via a control bus.
 6. The routing facilityaccording to claim 5, wherein said control bus is operable to beconnected to the main control unit via a plug-and-socket connection. 7.A subsea electronics module for a subsea control unit, the subseaelectronics module comprising a routing facility according to claim 1.8. A method for routing within a subsea electronics module, comprisingthe steps of: routing data packets between segments of a differentialserial bus through a single circuit board, and accessing at least one ofdigital and analogue process values via the differential serial bus andat least one input/output interface on said single circuit board.
 9. Themethod according to claim 8, comprising the step of providing a total ofthree input/output interfaces, namely a digital input interface, adigital output interface and an analogue input interface on said singlecircuit board.
 10. The method according to claim 8, comprising the stepof providing as said means for routing: a microcontroller a fieldprogrammable gate array and at least two router resources, each routerresource comprising a respective local transceiver for a differentialserial bus and a respective remote transceiver for the differentialserial bus, and comprising the step of connecting each local transceiverwith the corresponding remote transceiver and with said fieldprogrammable gate array that is able to route data packets between saidrouter resources.
 11. The method according to claim 8, comprising thestep of galvanically isolating each of said remote transceivers from thecorresponding local transceiver, wherein said remote transceivers arefloating and said local transceivers are related to a local electricalground, and wherein each of said remote transceivers comprises activebus termination means and bias means.
 12. The method according to claim8, comprising the step of connecting said microcontroller and said fieldprogrammable gate array to a main control unit of the subsea electronicsmodule via a control bus.
 13. The method according to claim 12,comprising the step of connecting said control bus to the main controlunit via a plug-and-socket connection.